The present invention relates generally to apparatus for providing reference light beams and, more particularly, to apparatus wherein three such beams simultaneously define two reference lines and an orthogonal reference plane.
Laser beam systems have been employed in numerous surveying and construction applications. In one such system, a laser beam projector device provides a rotating laser beam which establishes a reference plane. In use, the projector may, for example, be mounted at the desired height of a hanging ceiling in a building under construction. The beam is rotated in a horizontal plane to assist the workers in determining the proper height for the ceiling throughout the room.
The rotating laser beam provides a continuous, visible plane of light that creates a constant horizontal benchmark of elevation over the entire work area. Additionally, it allows the workers to check for low duct work, sprinklers, and other obstructions before setting the support grid for the ceiling. Such a horizontal reference plane is also advantageous in constructing raised access flooring. Typically, the laser projector device also can be positioned to provide a vertical reference plane of light, or a plane of light in other orientations. A laser projector device of this type can be used for laying out overhead drop walls and bulkheads, and in other construction operations.
U.S. Pat. Nos. 4,062,634; 4,035,085; and, 4,031,629 all disclose rotating laser beam projector devices. In each projector device, a generally horizontal rotating laser beam is produced by projecting a primary laser beam generally upward and then deflecting the beam by 90 degrees within a penta-mirror or pentaprism assembly. The pentaprism assembly is rotated about a vertical axis to cause the horizontal beam to rotate. In the past, some laser projector devices have included a removable pentaprism assembly. With such a projector device, the plane defined by the rotating beam could be aligned with a building structure, for example a wall, and the pentaprism assembly could thereafter be removed to produce a reference line normal to the wall.
U.S. Pat. No. 4,676,598 discloses a laser beam projector device which produces an upwardly extending, stationary reference beam and a rotating reference beam perpendicular thereto. With this laser projector device, pentaprism assembly removal is not necessary since the projector device produces an upwardly extending, stationary reference beam.
It has been found, however, that it is sometimes necessary to reference the upwardly extending, stationary reference beam and/or the rotating reference beam with a reference point located below the laser projector device on, for example, the floor of a structure under construction. A plumb bob hanging from a laser projector device has sometimes been used to provide a means for aligning the upwardly extending, stationary reference beam and/or the rotating reference beam with such a reference point. Hanging a plumb bob from a projector device, however, is not convenient and there is a risk that the plumb bob may be improperly positioned below the projector device, resulting in inaccuracies.
It is seen, therefore, that there is a need for a an improved laser beam projector device wherein an upwardly extending, stationary reference beam and/or a rotating reference beam may be accurately positioned with respect to a reference point located below the laser projector device.